For the last fifty years, the architecture of public buildings in the Western world has tended toward a design without windows which may be selectively opened by the occupants of various rooms and offices. The basic rationale was that climate control may be more easily effected without having to account for the idiosyncratic habits of various occupants of the building. In the last decade in the United States, the cost of energy to operate climate control equipment including heat and air conditioning has increased substantially.
While office buildings, schools and the like continue to be constructed with centralized climate control, most hotels and motels provide climate control selectively operable on a room-by-room basis. This commonly takes the form of window air conditioning or heat pump units provided in each room which may be operated by the occupant of the room to control the temperature and humidity therein.
Since hotel and motel rooms are almost uniformly rented at a flat rate per day, it has been difficult for the operators of these establishments to motivate their customers to be attentive to turning off climate control equipment when the room is unoccupied or when it is vacated. In particular, in the warmer climates a standardized "check-out time" tends to coincide with the warmest part of the day and many customers checking out of a hotel establishment will leave the air conditioning equipment on when they vacate the room.
Because of this confluence of construction practices and human habits, a number of designs for controlling climate control equipment remotely from a central location, particularly in hotels and motels, have been created. The common denominator of these designs is one which allows someone at a central control location, such as the desk of a hotel to turn off the climate control equipment when the room is vacated, and to turn it on upon the arrival of the next occupant.
Some arrangements have included switching schemes which required provision of separate wiring from the central location to the various rooms of the building. However, it is more common for arrangements for controlling climate control equipment on a room-by-room basis to be designed to be operable over a telephone network, particularly the extension lines of a private branch exchange (PBX) which are commonly found in such buildings. Since the conventional operation of hotels, motels and other buildings includes installation of a PBX telephone system, a number of switching arrangements have been designed to take advantage of the preexistence of the PBX network to turn air condition equipment on and off over the telephone lines. The present invention is an improved device of this type.
Previous switches controllable over the telephone lines have taken a number of forms. One arrangement uses a relay operable from the telephone line which is powered by charging a capacitor, inductively coupled to the telephone line when a ringing signal is placed on the phone line. When the ringing signal is applied, the inductive coupling provides charge to the capacitor which operates a break down device when the voltage reaches a predetermined level. Thus, power is supplied to the relay coil. The disadvantage of such an arrangement is that it requires a ringing signal to be applied to the telephone line to operate the device. If someone is present in the room and the ringing signal is applied, their natural inclination will be to answer the telephone unnecessarily, and possibly defeating operation of the device. The second disadvantage is that the device must be selectively decoupled when the room is occupied and the telephone is to be made available so that the application of a ringing signal indicates the actual existence of an incoming call.
Other arrangements have included rather complex tone control circuits in a time division multiplexing scheme for keeping the air conditioning equipment in selected rooms off. One such arrangement shows a circuit provided on each PBX extension in which receipt of a particular tone over the extension activates the monostable multivibrator to maintain a relay controlling the air conditioning equipment in an off state for a predetermined period of time. Failure to periodically reapply the tone signal to the PBX extension will cause the relay to drop off, thus allowing the air conditioning equipment to operate in a normal fashion. The basic disadvantage of such a system is that it requires that the PBX provide a rather complex signaling scheme for continuously applying the tone burst to the extension lines of unoccupied rooms in order to maintain equipment in its off state.
Furthermore, the device is disabled when the telephone goes off-hook. Thus, if employees of the establishment use the telephone extension for several minutes while the room is in an otherwise unoccupied state, the swiching device is disabled, and the air conditioning equipment may spuriously start up for several minutes. This constitutes a waste of the energy to operate the equipment since no effective cooling takes place.
Another arrangement uses the combination of a separate voltage source, often found to operate "message lights" on hotel telephones, combined with a reverse battery signal, to get a sum voltage sufficient to operate a relay to maintain the switch controlling the air conditioning in an off state.
Still another arrangement shows a remote control scheme remotely operable by conventional dual tone multifrequency tones. In this arrangement the remote control circuit must "answer" the telephone in order to respond to tones provided from the central location. Thus, it will be apparent that the device is inoperable when the telephone is in use.
Prior art tone operated devices have uniformly used signals within the normal band width of voice grade telephone lines. Thus, the use of such a switching device necessarily involves some interference with the normal function of the telephone. The prior art has not provided a remote switch controllable over a telephone line which is completely powered from the central office or PBX battery, and thus is strictly an add-on device requiring no separate external source of power. which provides control of climate conditioning equipment solely over preexisting telephone wiring; and which is operable irrespective of whether the telephone is on-hook or off-hook and which may further be operated when the telephone is in use without the user of the telephone having any awareness that the control function has taken place. Such an arrangement is provided by the present invention.